The invention is based on a method for determining the north direction or the travel direction of a vehicle having an electronic compass including a magnometer fixedly arranged in the vehicle and an evaluating circuit which cyclically receives the measurement values of the magnetic field vector effective at and measured by the magnetometer and processes the measurement values to check a predetermined elliptical locus diagram and to determine parameters of the travel direction and to correct the locus diagram during a deviation of several successive measurement values from a predetermined value of the locus diagram.
Such a method for correcting the elliptical locus diagram determined for the magnetic field vector effective at the magnetometer is known from German Offenlegungsschrift 3,509,548. In this document, it is proposed to check the values of the magnetic field, measured by the magnetometer, with respect to a deviation from the determined locus diagram and in each case then to perform a correction of the locus diagram whenever deviations of the measurement values from the locus diagram exceed a particular amount several times. The disadvantageous factor in this prior art method is that the angle errors in the direction indication, occurring due to magnetic field disturbances, are corrected only very inadequately and too slowly by this method.
In a heading measuring device known from German Patent Specification 2,651,678, the magnetic field sensor is caused to switch to a further sensor for correcting angle errors during the occurrence of magnetic field disturbances, if the values measured by the magnetic field sensor deviate from a nominal value by a predetermined amount. In this prior art arrangement, it is disadvantageous that an additional sensor is needed and at least partially is influenced by the earth's magnetic field and thus by external field disturbances.